WEATHERFAX AND THE RSP DUO RECEIVER - BASIC INFO
For completeness, some background information is necessary. The up to date list of Meteofax radio stations worldwide, with frequencies, technical data and transmission schedules, is dowloadable here in PDF form:http://www.nws.noaa.gov/os/marine/rfax.pdf
I still have a hardcopy specimen of April 1995.
Many Weather organisations publish their own detailed schedules. Daily schedule for the Deutscher Wetterdienst is transmitted along with weather information each day at 14:25 to 14:45 GMT and is also available below in PDF format:https://www.dwd.de/EN/specialusers/ship ... onFile&v=1
Meteofax HF transmission parameters (to be set on the decoding software) are as follows (Deuscher Wetterdienst abbreviated DW
Frequency and call sign:.................Example DW: DDK3/DDK6: 3885KHz / 7880 KHz / 13882.5 KHz.
Class of emission:.........................Example DW: F1C with +425Hz (white) and -425Hz (black).
Transmission mode reference...........USB or LSB for NORMAL. Example DW: USB/NORMAL.
Transmitted lines per minute (LPM)... 60, 90, 100, 120, 180, 240. Example DW: 120.
5 seconds start tone frequency.........IOC576/300 Hz. IOC288/675 Hz. Example DW: IOC576.
Phasing signal duration...................30 sec. Black pulses on a white line.
5 seconds stop tone frequency..........450 Hz.
In a Meteofax transmission, which is only black and white, the carrier is modulated with two tones, one at +425Hz for white and the other at -425Hz for black off center of this double amount from the nominal frequency. This means that if we look at the emission spectrum we shall see the carrier at -1900 Hz, shifting up 425 Hz and we can receive and decode the signal setting the receiver to USB or to LSB: if we chose the wrong sideband setting (tuning the receiver above the nominal frequency) white will become black and vice-versa, but there is always a software command for "NORMAL" or "REVERSE". Sometimes, with interference present, going to the "wrong" sideband setting can improve reception.
To set up our decoding software, we must make sure we have selected the relevant parameters. For the DW example, LPM=120; IOC576; USB. IOC is the Index of Cooperation and it is almost always set to the value of 576, corresponding to 300 Hz.
Supposing we are listening to DW, transmission starts with a 5" tone at 300 Hz which tells our software to get ready to receive, then we have 30" of phasing signal, then a variable duration time with no tones, then transmission. At the end we have a 5" stop tone at 450 Hz which stops the software and the received chart is stored. After a pause we may have or not have another transmission.
How to set it all up in the next post.